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- Homework Statement
- This isn't my actual homework question per se, I came upon this formula and I'm curious to know where it comes from.

- Relevant Equations
- R = p*h/pi*a*b and R = P*h/A

The actual homework question is about finding the voltage of a tapered wire, one where the two ends are different sizes (1cm and 2cm in this case). I've been searching for an equation to do this simply by just plugging in the values I have and I came across this.

Where
is resistivity, h is length of wire and a and b a radii of two cross sections

I've familiar with ph/A or pl/A but I've don't think I've ever seen it with Pi*a*b replace the A. I was wondering if anyone could just explain if this is in some book or it if it is derived from something else.

Thanks

Where

I've familiar with ph/A or pl/A but I've don't think I've ever seen it with Pi*a*b replace the A. I was wondering if anyone could just explain if this is in some book or it if it is derived from something else.

Thanks